Abstract: A circuit arrangement for correcting and controlling the attenuation characteristic of a communications transmission link by using adjustable attenuators in which a measuring transmitter produces a measuring signal of constant amplitude and at a frequency which is variable within the transmission frequency band and the signal is fed to an analysis device after passing through the communication transmission link so as to establish its frequency dependent amplitude variations and wherein the individual adjusting elements of the attenuators are consecutively actuated such that the amplitude variation in each case reaches a minimum value and the measuring transmitter can be consecutively switched to a series of individual frequencies which lie in frequency gaps between individual communication transmission channels and wherein digital storage means are utilized and wherein a rectifier produces a voltage which indicates the frequency dependent amplitude fluctuations of the signal to be measured.

Abstract: A selectively tunable heterodyne receiver including a plurality of frequency conversion stages which can be tuned to a desired receiving frequency by the use of two voltages which control the coarse and fine tuning adjustments and wherein the first voltage is supplied to a first injection oscillator to control the harmonic output of a crystal controlled harmonic generator and wherein the second voltage is supplied to a second injection oscillator which is continuously variable within a frequency range corresponding to the frequency spacing between the adjacent harmonics of the harmonic generator and wherein the second oscillator is stabilized to the desired adjusted frequency.